1. Field of the Invention
This invention relates to a motor driving apparatus suitably applied to a paper feeder for a facsimile, and more particularly to a power saving motor driving apparatus having an excellent rotational stability.
2. Description of the Prior Art
A facsimile is provided with a paper feeder as a means for transferring documents to be transmitted and a recording paper stored in the interior thereof.
This paper feeder usually employs a stepping motor as a driving motor therefor, and this motor is driven as its speed is controlled in accordance with the content of image data on a document to be transmitted and that of image data on a document to be received.
There are two types of known driving motor driving systems, which are a constant voltage driving system and a constant current chopping driving system.
In the constant voltage driving system, a driving motor is controlled so that a driving voltage applied thereto becomes constant, while, in the latter constant current chopping driving system, a driving motor is driven so that the level of a detected electric current flowing through a motor coil becomes constant, whereby the driving motor is controlled so as to attain a constant motor torque.
In the constant current chopping driving system out of such motor driving systems, the operational stability of a motor during the low speed rotation thereof is ensured but the constant current control accuracy varies depending upon the detecting accuracy of a circuit for detecting the electric current flowing through a motor coil, so that the motor torque varies greatly when the degree of variation of this control accuracy is high.
Since this driving motor driving system is based on a closed circuit control operation, it is necessary as generally known that a DC amplifier and a transfer characteristic-determining filter be provided in the closed circuit for each phase of the motor coil. This causes the circuit structure to be complicated.
In the constant voltage driving system, the operational stability of a driving motor during the high speed rotation is high but a power loss due to the thermal energy occurring during the low speed rotation of the motor becomes large.